A nonvolatile semiconductor memory device typified by a NAND flash memory generally includes a memory cell region and a peripheral region provided outside the memory cell region on a semiconductor substrate. The memory cell region includes an element isolation region electrically insulating each element. Also in the peripheral region, an element isolation region defining an element or the like is provided.
For both element isolation regions, in general, the element isolation region in the memory cell region is formed shallow and the element isolation region in the peripheral region is formed deep due to the micro-loading effect. To suppress the current leak between cells in the memory cell region, the element isolation region in the memory cell region is deep preferably. However, as the element isolation region in the memory cell region is deeper, the volume of the element isolation region in the peripheral region becomes larger. Therefore, when an insulating film with large contraction stress or compressive stress is formed in the element isolation region in the peripheral region, the semiconductor substrate may receive stress from the element isolation region and a defect may occur in the semiconductor substrate. Consequently, the reliability of the nonvolatile semiconductor memory device may be reduced.